1. Field of the Invention
This invention relates to a far infrared ray emitting body, and, more particularly, to a far infrared ray emitting body which as itself or combined with other substances can provide far infrared radiation to various objects to effect excitation vibration of water molecules in the objects. The far infrared ray emitting body has a wide variety of uses in the fields of drying, heating, food processing, plant growth, health promotion, and the like.
2. Description of the Background
Among various far infrared ray emitting bodies, papers and woods cannot be used at a high temperature because of their ready combustibility. Metals exhibit only a small radiation activity. Ceramics which are inorganic oxides are considered as the most effective far infrared ray emitting bodies. A number of studies on ceramic far infrared ray emitting bodies have been reported, including zirconia, titania, alumina, as well as low-thermal expansion materials such as cordierite, .beta.-spodumene, aluminum titanate, and the like. Ceramics which are considered the most effective far infrared ray emitting bodies at the present time are oxides of transition elements such as MnO.sub.2, Fe.sub.2 O.sub.3, CuO, CoO, and the like, or ceramics obtained by mixing these transition element oxides with Kibushi-Nendo (a clay) or petarite, as a low-thermal expansion material, and by calcining the mixture at above 1,000.degree. C. These materials are very close to a black body exhibiting a high degree of radiation activity throughout the entire infrared range.
Various far infrared ray emitting bodies are on the market, including those mentioned above as well as naturally occurring materials. Their qualities, far infrared radiation capacities, and production costs remain, however, to be improved.
The present inventors have undertaken extensive studies to develop a far infrared ray emitting body possessing a stronger radiation capacity. The studies have been concentrated on various kinds of powders of inorganic materials, especially on their particle sizes, particle size distributions, and the effect of these factors on their far infrared radiation capacities. As a result, the inventors found that an inorganic powder emitted far infrared rays of a higher strength when the powder was more particulate and its particle size was more closely distributed. This finding has matured into a far infrared ray emitting body comprising a base material or a core material having an ultrafine inorganic powder with a closely distributed particle size adhered on said base or core material.
Further studies by the inventors revealed that alumina and silica are the most effective inorganic powders for adherence onto core materials, and that the most effective far infrared radiation could be obtained when the inorganic powders had a particle size below 500 angstrom, and preferably below 200 angstrom. That is to say, the body having an uneven, large specific surface area provides a larger radiation effect. The far infrared ray emitting body exhibited a considerable radiation capacity without a calcining process.